Boolean operators like “OR” and “AND” allow you to combine keywords to produce more relevant results.

First, let’s look at OR.

OR works well for combining synonyms or similar terms.

So, imagine these are articles about jam, and these are articles about jelly. If we OR these terms together, we will get everything in the circles, whether it's articles about just jam, articles just jelly, or both.

Now, let’s look at AND.

AND works well for combining different concepts. So, imagine that these are articles about peanut butter and these are articles about jam OR jelly. If we AND these together, we will get everything in the overlapping circles, which is articles about both peanut butter AND jam OR jelly.

So how does this work in an actual search?

In the example above, our final search might be: “peanut butter” AND (jam OR jelly)

Generally, you need to capitalize your Boolean operators in a database. The double quotations around “peanut butter” keeps these words together, and the brackets around (jam OR jelly) means that these will be OR’d together before they are AND’d with “peanut butter”.

This is similar to how mathematical equations work, where the results depend on where you put the brackets.

For example, if you have 1 plus 2 times 3, this can equal 7, or if you put brackets around 1 plus 2, it can actually equal 9.

Now let’s say your research question is: Does exposure to peanuts in childhood affect the development of allergies?

The main concepts are peanuts, childhood and allergies.

Let’s start with peanut (with a star). This will search for peanut and peanuts. The star acts like a ‘wild card’.

Our next concept is childhood. We could search this using child with a star, which would find child, children, and childhood. We could also search for similar terms such as young or youth.

These we would want to OR together and keep in brackets so that these terms stay together.

Our final concept, allergy, we would search with a star which would find allergy, allergies, allergenic, and allergic.

Finally, we would want to AND all of our different concepts together.

Now we have a complete Boolean search that you can use in any database.